Residential and commercial irrigation systems typically include one or more solenoid operated valves that are turned ON and OFF by an electronic irrigation controller. The valves admit water to various subterranean branch lines usually made of PVC pipe that typically have several sprinklers connected to risers coupled to the branch lines at spaced intervals. Each combination of a solenoid valve and its associated sprinklers is referred to in the irrigation industry as a station or zone. A modern electronic irrigation controller typically includes a microprocessor and separate memory, or a micro-computer with on-chip memory, that stores and executes one or more watering programs. The watering programs can be pre-programmed by the user via push button and/or rotary controls. The controller usually has an LCD or other display to facilitate programming by the user. The microprocessor controls the solenoid valves via suitable drivers and switching devices. The valves are opened and closed by the microprocessor in accordance with the pre-programmed run and cycle times for each of the stations.
Over the past decade, modular irrigation controllers have gained increasing popularity. In these controllers, the base portion of the system contains the microprocessor and user actuated controls. Each station is then controlled by a corresponding station module which comprises a plastic housing that encloses and supports a station module circuit, as well as wire connection terminals for connecting wires to a plurality of solenoid actuated valves. Typically each station module can independently control more than one solenoid actuated valve, i.e., station. The station modules contain pins, sockets, card edge connectors or some other standard form of electro-mechanical connectors for establishing electrical connections when the station modules are inserted into slots or receptacles in either the housing that contains the microprocessor or a separate back panel hinged to the microprocessor housing.
The advantage of a modular irrigation controller is that initially it need only be equipped with the minimum number of station modules that can control the total number of stations designed into the irrigation system from the outset. Thus, for example, an irrigation system may have only three zones, requiring only a single station module, while another may have twelve stations which might require four station modules. Considerable cost savings are thus achieved and less inventory of different sizes of irrigation controllers needs to be maintained by distributors. Moreover, if an irrigation system expands after initial installation because the landscaping has increased, additional station modules can readily be added. Also, station modules can be removed and replaced if damaged, for example, during a lightening strike.
When the station modules are plugged into the receptacles of a modular expandable irrigation controller they are mechanically supported and an electrical connection is made between the microprocessor and the driver. It has been conventional to use plastic spring members or elements to hold the station modules in place in their respective receptacles or slots. However, such springs often require considerable force to be exerted by the user, both during installation and withdrawal of the station modules. The spring members can also break and difficulties have been encountered in ensuring that a complete and positive electrical connection is both achieved and maintained. In some cases, station module installation can lead to breakage in the metal pins or metal leaf spring contacts used to make the electrical connection.